U.S. patent application number 11/007261 was filed with the patent office on 2005-06-30 for polycrystalline diamond abrasive elements.
Invention is credited to Achilles, Roy Derrick, Lancaster, Brett, Parker, Imraan, Roberts, Bronwyn Annette, Tank, Klaus.
Application Number | 20050139397 11/007261 |
Document ID | / |
Family ID | 34701591 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050139397 |
Kind Code |
A1 |
Achilles, Roy Derrick ; et
al. |
June 30, 2005 |
Polycrystalline diamond abrasive elements
Abstract
A polycrystalline diamond abrasive element, particularly a
cutting element, comprises a layer of polycrystalline diamond
having a working surface and bonded to a substrate, particularly a
cemented carbide substrate, along an interface. The polycrystalline
diamond abrasive element is characterised by using a binder phase
that is homogeneously distributed through the polycrystalline
diamond layer and that is of a fine scale. The polycrystalline
diamond also has a region adjacent the working surface lean in
catalysing material and a region rich in catalysing material.
Inventors: |
Achilles, Roy Derrick;
(Bedfordview, ZA) ; Roberts, Bronwyn Annette;
(Parkhurst, ZA) ; Parker, Imraan; (Rylands Estate,
ZA) ; Lancaster, Brett; (Boksburg, ZA) ; Tank,
Klaus; (Johannesburg, ZA) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
34701591 |
Appl. No.: |
11/007261 |
Filed: |
December 9, 2004 |
Current U.S.
Class: |
175/434 ;
175/426 |
Current CPC
Class: |
B22F 7/02 20130101; Y10T
428/252 20150115; C22C 26/00 20130101; Y10T 428/30 20150115; B22F
2998/00 20130101; E21B 10/567 20130101; B22F 2998/00 20130101; B22F
2207/03 20130101 |
Class at
Publication: |
175/434 ;
175/426 |
International
Class: |
E21B 010/36 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 11, 2003 |
ZA |
2003/09629 |
Claims
We claim:
1. A polycrystalline diamond abrasive element, comprising a layer
of polycrystalline diamond, which has a binder phase containing
catalysing material, having a working surface and bonded to a
substrate along an interface, the polycrystalline diamond abrasive
element being characterised by the binder phase being homogeneously
distributed through the polycrystalline diamond layer and being of
a fine scale and the polycrystalline diamond having a region
adjacent the working surface lean in catalysing material and a
region rich in catalysing material.
2. A polycrystalline diamond abrasive element according to claim 1,
wherein the binder phase distribution is expressed as the binder
phase thicknesses or mean free path measurements in the
microstructure of the binder phase, which are less than 6
.mu.m.
3. A polycrystalline diamond abrasive element according to claim 2,
wherein the binder phase thicknesses or mean free path measurements
in the microstructure of the binder phase are less than 4.5
.mu.m.
4. A polycrystalline diamond abrasive element according to claim 3,
wherein the binder phase thicknesses or mean free path measurements
in the microstructure of the binder phase are less than 3
.mu.m.
5. A polycrystalline diamond abrasive element according to claim 2,
wherein the standard deviation of the binder phase thicknesses,
expressed as a percentage of the average binder phase thickness, is
less than 80%.
6. A polycrystalline diamond abrasive element according to claim 5,
wherein the standard deviation of the binder phase thicknesses is
less than 70%.
7. A polycrystalline diamond abrasive element according to claim 6,
wherein the standard deviation of the binder phase thicknesses is
less than 60%.
8. A polycrystalline diamond abrasive element according to claim 1,
wherein the binder phase distribution is expressed in terms of an
equivalent circle diameter, the standard deviation of the
distribution of circle diameters being less than 80%.
9. A polycrystalline diamond abrasive element according to claim 8,
wherein the standard deviation of the distribution of circle
diameters is less than 70%.
10. A polycrystalline diamond abrasive element according to claim
9, wherein the standard deviation of the distribution of circle
diameters is less than 60%.
11. A polycrystalline diamond abrasive element according to claim
1, wherein the polycrystalline diamond is formed from diamond
particles having an average particle grain size of less than 20
microns.
12. A polycrystalline diamond abrasive element according to claim
11, wherein the polycrystalline diamond is formed from diamond
particles having an average particle grain size of less than 15
microns.
13. A polycrystalline diamond abrasive element according to claim
12, wherein the polycrystalline diamond is formed from diamond
particles having an average particle grain size of less than 11
microns.
14. A polycrystalline diamond abrasive element according to claim
1, wherein the polycrystalline diamond has a wear ratio, determined
in a manner as defined herein, of less than 50%.
15. A polycrystalline diamond abrasive element according to claim
14, wherein the polycrystalline diamond has a wear ratio of less
than 40%.
16. A polycrystalline diamond abrasive element according to claim
15, wherein the polycrystalline diamond has a wear ratio of less
than 30%.
17. A polycrystalline diamond abrasive element according to claim
1, wherein the polycrystalline diamond is produced from a mass of
diamond particles having at least three different average particle
sizes.
18. A polycrystalline diamond abrasive element according to claim
17, wherein the polycrystalline diamond is produced from a mass of
diamond particles having at least five different average particle
sizes.
19. A polycrystalline diamond abrasive element according to claim
1, which is a cutting element.
20. A polycrystalline diamond abrasive element according to claim
1, wherein the substrate is a cemented carbide substrate.
21. A polycrystalline diamond abrasive element according to claim
1, wherein the region lean in catalysing material extends into the
polycrystalline diamond from the working surface to a depth of from
about 30 microns to about 500 microns.
22. A polycrystalline diamond abrasive element according to claim
21, wherein the region lean in catalysing material extends to a
depth of from about 60 microns to about 350 microns.
23. A polycrystalline diamond abrasive element according to claim
1, wherein the working surface of the polycrystalline diamond layer
defines a cutting edge that is bevelled.
24. A polycrystalline diamond abrasive element according to claim
23, wherein the region lean in catalysing material follows the
bevelled cutting edge.
25. A method of producing a polycrystalline diamond abrasive
element according to claim 1, the method including the steps of
creating an unbonded assembly by providing a substrate, placing a
mass of diamond particles and a binder phase on a surface of the
substrate, the binder phase being arranged such that it is
homogeneously distributed in the unbonded assembly, and providing a
source of catalysing material for the diamond particles, subjecting
the unbonded assembly to conditions of elevated temperature and
pressure suitable for producing a polycrystalline diamond layer of
the mass of diamond particles, such layer being bonded to the
substrate, and removing catalysing material from a region of the
polycrystalline diamond layer adjacent an exposed surface
thereof.
26. A method according to claim 25, wherein the substrate is a
cemented carbide substrate.
27. A method according to claim 26, wherein the cemented carbide
substrate is the source of catalysing material.
28. A method according to any one of claims 27, wherein additional
catalysing material is mixed in with the mass of diamond particles.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to tool inserts and more particularly
to cutting tool inserts for use in drilling and coring holes in
subterranean formations.
[0002] A commonly used cutting tool insert for drill bits is one
which comprises a layer of polycrystalline diamond (PCD) bonded to
a cemented carbide substrate. The layer of PCD presents a working
face and a cutting edge around a portion of the periphery of the
working surface.
[0003] Polycrystalline diamond, also known as a diamond abrasive
compact, comprises a mass of diamond particles containing a
substantial amount of direct diamond-to-diamond bonding.
Polycrystalline diamond will generally have a second phase which
contains a diamond catalyst/solvent such as cobalt, nickel, iron or
an alloy containing one or more such metals.
[0004] In drilling operations, such a cutting tool insert is
subjected to heavy loads and high temperatures at various stages of
its life. In the early stages of drilling, when the sharp cutting
edge of the insert contacts the subterranean formation, the cutting
tool is subjected to large contact pressures. This results in the
possibility of a number of fracture processes such as fatigue
cracking being initiated.
[0005] As the cutting edge of the insert wears, the contact
pressure decreases and is generally too low to cause high energy
failures. However, this pressure can still propagate cracks
initiated under high contact pressures; and can eventually result
in spalling-type failures.
[0006] In the drilling industry, PCD cutter performance is
determined by a cutter's ability to both achieve high penetration
rates in increasingly demanding environments, and still retain a
good condition post-drilling (hence enabling re-use). In any
drilling application, cutters may wear through a combination of
smooth, abrasive type wear and spalling/chipping type wear. Whilst
a smooth, abrasive wear mode is desirable because it delivers
maximum benefit from the highly wear-resistant PCD material,
spalling or chipping type wear is unfavourable. Even fairly minimal
fracture damage of this type can have a deleterious effect on both
cutting life and performance.
[0007] With spalling-type wear, cutting efficiency can be rapidly
reduced as the rate of penetration of the drill bit into the
formation is slowed. Once chipping begins, the amount of damage to
the diamond table continually increases, as a result of the
increased normal force now required to achieve a given depth of
cut. Therefore, as cutter damage occurs and the rate of penetration
of the drill bit decreases, the response of increasing weight on
bit can quickly lead to further degradation and ultimately
catastrophic failure of the chipped cutting element.
[0008] In optimising PCD cutter performance increasing wear
resistance (in order to achieve better cutter life) is typically
achieved by manipulating variables such as average diamond grain
size, overall catalyst/solvent content, diamond density and the
like. Typically, however, as PCD material is made more wear
resistant it becomes more brittle or prone to fracture. PCD
elements designed for improved wear performance will therefore tend
to have poor impact strength or reduced resistance to spalling.
This trade-off between the properties of impact resistance and wear
resistance makes designing optimised PCD structures, particularly
for demanding applications, inherently self-limiting.
[0009] If the chipping behaviours of more wear resistant PCD can be
eliminated or controlled, then the potentially improved performance
of these types of a PCD cutters can be more fully realised.
[0010] Previously, modification of the cutting edge geometry by
bevelling was perceived to be a promising approach to reducing this
chipping behaviour.
[0011] It has been shown (U.S. Pat. No. 5,437,343 and U.S. Pat. No.
5,016,718) that pre-bevelling or rounding the cutting edge of the
PCD table significantly reduces the spalling tendency of the
diamond cutting table. This rounding, by increasing the contact
area, reduces the effect of the initial high stresses generated
during loading when the insert contacts the earthen formation.
However, this chamfered edge wears away during use of the PCD
cutter and eventually a point is reached where no bevel remains. At
this point, the resistance of the cutting edge to spalling-type
wear will be reduced to that of the unprotected/unbevelled PCD
material.
[0012] U.S. Pat. No. 5,135,061 suggests that spalling-type
behaviour can also be controlled by manufacturing the cutter with
the cutting face formed of a layer of PCD material which is less
wear resistant than the underlying PCD material(s), hence reducing
its tendency to spall. The greater wear of the less wear resistant
layer in the region of the cutting edge provides a rounded edge to
the cutting element where it engages the formation. The rounding of
the cutting edge achieved by this invention hence has a similar
anti-spalling effect to bevelling. The advantages of this approach
can be significantly outweighed by the technical difficulty of
achieving a satisfactorily thin, less wear resistant layer in situ
during the synthesis process. (The consistent and controlled
behaviour of this anti-spalling layer is obviously highly dependant
on the resultant geometry). In addition, the reduced wear
resistance of this upper layer can begin to compromise the overall
wear resistance of the cutter--resulting in a more rapid bluntening
of the cutting edge and sub-optimal performance.
[0013] JP 59119500 claims an improvement in the performance of PCD
sintered materials after a chemical treatment of the working
surface. This treatment dissolves and removes the catalyst/solvent
matrix in an area immediately adjacent to the working surface. The
invention is claimed to increase the thermal resistance of the PCD
material in the region where the matrix has been removed without
compromising the strength of the sintered diamond.
[0014] A PCD cutting element has recently been introduced on to the
market which is said to have improved wear resistance without loss
of impact strength. United States patents U.S. Pat. Nos. 6,544,308
and 6,562,462 describe the manufacture and behaviour of such
cutters. The PCD cutting element is characterised inter alia by a
region adjacent the cutting surface which is substantially free of
catalysing material. The improvement of performance of these
cutters is ascribed to an increase in the wear resistance of the
PCD in this area; where the removal of the catalyst material
results in decreased thermal degradation of the PCD in the
application.
SUMMARY OF THE INVENTION
[0015] According to the present invention, there is provided a
polycrystalline diamond abrasive element, particularly a cutting
element, comprising a layer of polycrystalline diamond, which has a
binder phase containing catalysing material, having a working
surface and bonded to a substrate, particularly a cemented carbide
substrate, along an interface, the polycrystalline diamond abrasive
element being characterised by the binder phase being homogeneously
distributed through the polycrystalline diamond layer and being of
a fine scale and the polycrystalline diamond having a region
adjacent the working surface lean in catalysing material and a
region rich in catalysing material.
[0016] The distribution of the binder phase thicknesses or mean
free path measurements in the microstructure has an average which
is preferably less than 6 .mu.m, more preferably less than 4.5
.mu.m and most preferably less than 3 .mu.m.
[0017] In addition, the standard deviation of the distribution of
the binder phase thicknesses, expressed as a percentage of the
average binder phase thickness, is less than 80%, more preferably
less than 70%, and most preferably less than 60%.
[0018] Where the distribution of the binder phase can be expressed
in terms of an "equivalent circle diameter", the standard deviation
of the distribution of circle diameters, expressed as a percentage
of the average circle diameter, is preferably less than 80%, more
preferably less than 70%, and most preferably less than 60%.
[0019] Due to the homogeneous distribution and fine scale of the
binder phase, also referred to as the catalyst/solvent matrix, the
polycrystalline diamond is of a "high grade".
[0020] In addition, the "high grade" polycrystalline diamond is a
polycrystalline diamond material characterized by one or more of
the following:
[0021] 1) having an average diamond particle grain size of less
than 20 microns, preferably less than 15 microns, even more
preferably less than about 11 microns;
[0022] 2) a very high wear resistance i.e. a wear resistance which
is sufficiently high to render a polycrystalline diamond abrasive
element using such a material, in the absence of a region adjacent
the working surface lean in catalysing material, highly susceptible
to spalling or chipping type wear; and
[0023] 3) a wear ratio, being the percentage ratio of the quantity
of material removed from a polycrystalline diamond abrasive element
having a region adjacent the working surface lean in catalysing
material relative to the size of the wear scar of or the quantity
of material removed from a polycrystalline diamond abrasive
element, made of the same grade polycrystalline diamond, but in the
absence of a region adjacent the working surface lean in catalysing
material, of less than 50%, preferably less than 40%, more
preferably less than 30%, in the latter stages of a conventional
application-based granite boring mill test.
[0024] The polycrystalline diamond has a very high wear resistance.
This may be achieved, and is preferably achieved in one embodiment
of the invention, by producing the polycrystalline diamond from a
mass of diamond particles having at least three, and preferably at
least five different average particle sizes. The diamond particles
in this mix of diamond particles are preferably fine.
[0025] In polycrystalline diamond, individual diamond particles
are, to a large extent, bonded to adjacent particles through
diamond bridges or necks. The individual diamond particles retain
their identity, or generally have different orientations. The
average particle size of these individual diamond particles may be
determined using image analysis techniques. Images are collected on
the scanning electron microscope and are analysed using standard
image analysis techniques. From these images, it is possible to
extract a representative diamond particle size distribution.
[0026] The polycrystalline diamond layer has a region adjacent the
working surface which is lean in catalysing material. Generally,
this region will be substantially free of catalysing material. The
region will extend into the polycrystalline diamond from the
working surface generally to a depth of as low as about 30 .mu.m to
no more than about 500 microns.
[0027] The polycrystalline diamond also has a region rich in
catalysing material. The catalysing material is present as a
sintering agent in the manufacture of the polycrystalline diamond
layer. Any diamond catalysing material known in the art may be
used. Preferred catalysing materials are Group VIII transition
metals such as cobalt and nickel. The region rich in catalysing
material will generally have an interface with the region lean in
catalysing material and extend to the interface with the
substrate.
[0028] The region rich in catalysing material may itself comprise
more than one region. The regions may differ in average particle
size, as well as in chemical composition. These regions, when
provided, will generally lie in planes parallel to the working
surface of the polycrystalline diamond layer.
[0029] According to another aspect of the invention, a method of
producing a PCD abrasive element as described above includes the
steps of creating an unbonded assembly by providing a substrate,
placing a mass of diamond particles and a binder phase on a surface
of the substrate, the binder phase being arranged such that it is
homogeneously distributed in the unbonded assembly, and providing a
source of catalysing material for the diamond particles, subjecting
the unbonded assembly to conditions of elevated temperature and
pressure suitable for producing a polycrystalline diamond layer of
the mass of diamond particles, such layer being bonded to the
substrate, and removing catalysing material from a region of the
polycrystalline diamond layer adjacent an exposed surface
thereof.
[0030] The substrate will generally be a cemented carbide
substrate. The source of catalysing material will generally be the
cemented carbide substrate. Some additional catalysing material may
be mixed in with the diamond particles.
[0031] The diamond particles contain particles having different
average particle sizes. The term "average particle size" means that
a major amount of particles will be close to the particle size,
although there will be some particles above and some particles
below the specified size. The peak and distribution of the
particles will have the specified size. Thus, for example, if the
average particle size is 10 microns, there will be some particles
that are larger and some particles which are smaller than 10
microns, but the major amount of the particles will be at
approximately 10 microns in size and a peak in the distribution of
the particles will be 10 microns.
[0032] The mass of diamond particles may have regions or layers
that differ from each other in their mix of diamond particles.
Thus, there may be a region or layer containing particles having at
least five different average particle sizes on a region or layer
that has particles having at least four different average particle
sizes.
[0033] Catalysing material is removed from a region of the
polycrystalline diamond layer adjacent an exposed surface thereof.
Generally, that surface will be on a side of the polycrystalline
layer opposite to the substrate and will provide a working surface
for the polycrystalline diamond layer. Removal of the catalysing
material may be carried out using methods known in the art such as
electrolytic etching, acid leaching and evaporation techniques.
[0034] The conditions of elevated temperature and pressure
necessary to produce the polycrystalline diamond layer from a mass
of diamond particles are well known in the art. Typically, these
conditions are pressures in the range 4 to 8 GPa and temperatures
in the range 1300 to 1700.degree. C.
[0035] It has been found that the PCD abrasive elements of the
invention have significantly improved wear behaviour, as a result
of controlling the spalling and chipping wear component, than PCD
abrasive elements of the prior art.
BRIEF DESCRIPTION OF THE DRAWING
[0036] The accompanying drawing is a graph showing comparative data
in a boring mill test using different polycrystalline diamond
cutting elements.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The polycrystalline diamond abrasive elements of the
invention have particular application as cutter elements for drill
bits. In this application, they have been found to have excellent
wear resistance and impact strength without being susceptible to
spalling or chipping. These properties allow them to be used
effectively in drilling or boring of subterranean formations having
high compressive strength.
[0038] A polycrystalline diamond layer is bonded to a substrate.
The polycrystalline diamond layer has an upper working surface
around which is a peripheral cutting edge. The polycrystalline
diamond layer has a region rich in catalysing material and a region
lean in catalysing material. The region lean in catalysing material
extends from the working surface into the polycrystalline diamond
layer. The depth of this region will typically be no more than
about 500 microns, and is preferably from about 30 to about 400
microns, most preferably from about 60 to about 350 microns.
Typically, if the PCD edge is bevelled, the region lean in
catalysing material will generally follow the shape of this bevel
and extend along the length of the bevel. The balance of the
polycrystalline layer extending to the cemented carbide substrate
is the region rich in catalysing material. In addition, the surface
of the PCD element may be mechanically polished so as to achieve a
low-friction surface or finish.
[0039] Generally, the layer of polycrystalline diamond will be
produced and bonded to the cemented carbide substrate in a HPHT
process. In so doing, it is important to ensure that the binder
phase and diamond particles are arranged such that the binder phase
is distributed homogeneously and is of a fine scale.
[0040] The homogeneity or uniformity of the structure is defined by
conducting a statistical evaluation of a large number of collected
images. The distribution of the binder phase, which is easily
distinguishable from that of the diamond phase using electron
microscopy, can then be measured in a method similar to that
disclosed in EP 0974566. This method allows a statistical evalution
of the average thicknesses of the binder phase along several
arbitrarily drawn lines through the microstructure. This binder
thickness measurement is also referred to as the "mean free path"
by those skilled in the art. For two materials of similar overall
composition or binder content and average diamond grain size, the
material which has the smaller average thickness will tend to be
more homogenous, as this implies a "finer scale" distribution of
the binder in the diamond phase. In addition, the smaller the
standard deviation of this measurement, the more homogenous is the
structure. A large standard deviation implies that the binder
thickness varies widely over the microstructure, i.e. that the
structure is not even, but contains widely dissimilar structure
types.
[0041] Another parallel technique, known as "equivalent circle
diameter", estimates a circle equivalent in size for each
individual microscopic area identified to be binder phase in the
microstructure. The collected distribution of these circles is then
evaluated statistically. In much the same way as for the mean free
path technique, the larger the standard deviation of this
measurement, the less homogenous is the structure. These two image
analysis techniques combine well to give an overall picture of the
homogeneity of the microstructure.
[0042] The diamond particles will preferably comprise a mix of
diamond particles, differing in average particle sizes. In one
embodiment, the mix comprises particles having five different
average particle sizes as follows:
1 Average Particle Size (in microns) Percent by mass 20 to 25
(preferably 22) 25 to 30 (preferably 28) 10 to 15 (preferably 12)
40 to 50 (preferably 44) 5 to 8 (preferably 6) 5 to 10 (preferably
7) 3 to 5 (preferably 4) 15 to 20 (preferably 16) less than 4
(preferably 2) Less than 8 (preferably 5)
[0043] In another embodiment, the polycrystalline diamond layer
comprises two layers differing in their mix of particles. The first
layer, adjacent the working surface, has a mix of particles of the
type described above. The second layer, located between the first
layer and the substrate, is one in which (i) the majority of the
particles have an average particle size in the range 10 to 100
microns, and consists of at least three different average particle
sizes and (ii) at least 4 percent by mass of particles have an
average particle size of less than 10 microns. Both the diamond
mixes for the first and second layers may also contain admixed
catalyst material.
[0044] Once the polycrystalline diamond abrasive element is formed,
catalysing material is removed from the working surface of the
particular embodiment using any one of a number of known methods.
One such method is the use of a hot mineral acid leach, for example
a hot hydrochloric acid leach. Typically, the temperature of the
acid will be about 110.degree. C. and the leaching times will be 3
to 60 hours. The area of the polycrystalline diamond layer which is
intended not to be leached and the carbide substrate will be
suitably masked with acid resistant material.
[0045] Two polycrystalline diamond cutter elements of the bi-layer
type described above were produced on respective cemented carbide
substrates. These polycrystalline diamond cutter elements will be
designated "A1U" and "A2U", respectively.
[0046] A further two polycrystalline diamond elements were produced
on respective cemented carbide substrates using the same diamond
mixes used in producing the polycrystalline diamond layers in A1U
and A2U. These polycrystalline diamond cutter elements will be
designated "A1L" and "A2L", respectively.
[0047] Each of the polycrystalline diamond elements A1L and A2L had
catalysing material, in this case cobalt, removed from the working
surface thereof to create a region lean in catalysing material.
This region extended below the working surface to an average depth
of about 250 .mu.m. Typically, the range for this depth will be
+/-40 .mu.m, giving a range of 210-290 .mu.m for the region lean in
catalysing material across a single cutter.
[0048] The cutter elements A1U, A2U, A1L and A2L were then compared
in a vertical boring mill test with a commercially available
polycrystalline diamond cutter element having a region immediately
below the working surface lean in catalysing material. In this
test, the relative quantity of PDC material removed was measured as
a function of the distance travelled by the cutter element boring
into the workpiece, which in this case was SW granite, in a boring
mill test. The results obtained are illustrated graphically by FIG.
1.
[0049] The commercially available polycrystalline diamond cutting
element is designated as "Prior Art 1L". It will be noted from FIG.
1 that a much larger quantity of PDC material was removed from the
prior art cutter element and the reference cutters A1U and A2U than
the cutter elements A1L and A2L of the invention in the latter
stages of the test. In the case of A1U and A2U, the greater
quantity of PDC material removed is ascribed to spalling/chipping
type wear due to their inherent high wear resistance. This will
necessitate an increase in weight on bit in order to achieve an
acceptable rate of cutting. This in turn induces higher stresses
within the cutter elements, resulting in a further reduction in
life. Even after extended boring, the cutter elements A1L and A2L
had not had significant quantities of PDC material removed.
[0050] The spread of behaviours in the reference untreated cutters
A1U and A2U is not unexpected and can be attributed to the
stochastic nature of the spalling type failure that these cutters
undergo. This behaviour is typical where a spalling/chipping
material removal mechanism dominates. By contrast, A1L and A2L show
very similar wear progression, indicating that a smooth type wear
is the dominant mechanism after carrying out the treatment.
[0051] The microstructures of the cutters employed in this test
were assessed using a scanning electron microscope. The
microstructural parameters measured were as set out in Table 1.
2TABLE 1 A1 A2 Cutter (U and L) (U and L) Prior Art L Binder
content distribution Area (%) 8.53% 8.75% 8.28% .sigma.* (%) 0.35%
0.40% 0.69% Binder thickness (or mean free path) distribution
Average (.mu.m) 2.10 2.17 10.8 .sigma.* (.mu.m) 0.98 1.17 9.00
.sigma.* (expressed as % of average) 46% 54% 83% Binder "equivalent
circle diameter" distribution Average 1.94 2.03 3.76 .sigma.*
(.mu.m) 1.06 0.87 4.07 .sigma.* (expressed as % of average) 55% 43%
108% .sigma.* is the statistical standard deviation of the
distribution
* * * * *